TPS2557-Q1: Maximum thermal shutdown temperature

Hi,

How is this situation?

Best Regards,
Kuramochi

Hi, Kuramochi-san,

The max recommend operation Tj is 125deg and OTSD Tj is 155deg. The part can work between 125deg to 155deg, but may cause life span loss. With the OTSD function, the part can never operate above 155deg.

Could you tell me why you need this data?

Regards,
Bob

Hi, Bob-san,

Thank you for your reply.

They need this data because the end customer seems to worry that OTSD overs absolute maximum voltage.

So we would like to know not the max recommended operation Tj but absolute maximum Tj.

Best Regards,

Kuramochi

Kuramochi-san,

What do you mean "OTSD overs absolute maximum voltage"?

Absolute maximum Tj is over OTSD threshold, so the part can't achieve maximum Tj during operation.

Regards,
Bob

Bob-san,

>Absolute maximum Tj is over OTSD threshold, so the part can't achieve maximum Tj during operation.

Is it guaranteed?
I'm thinking that it isn't guarantee because OTSD threshold is specified only min. value only.

Best Regards,
Kuramochi

Hi, Kuramochi-san,

Yes, it's guaranteed. I think the Abs max Tj should be a temperature that higher than max value of OTSD threshold. This way we can guarantee that part will never damaged of heat.

For example, you mentioned about TPS25810 in another threshold that its OTSD is 155deg and abs max Tj is 180deg. I have send mail to the engineer who wrote TPS25810 datasheet to confirm my conclusion above.

Regards,
Bob

Bob-san,

Thank you for your information and coorpolation.
Though I let my customer know your information, they were not satisfied.

When VBUS-GND are shorted, TPS2557-Q1 repeats OTSD and restart.
So high temperature condition may keep during long term.
My customer must show what the device doesn't damage on this condition for END customer.
To prove, they need the absolute maximum Tj and maximum OTSD value.
Could you please provide these data?

Best Regards,
Kuramochi

I have send e-mail to the designer, I am waiting for his ideas about it.

As far as the data, we don't have the data. I will see if designer can give some insight of it. If he can guarantee Tj can't exceed max Tj with OTSD(Absolute maximum Tj is over OTSD threshold), I think that's enough.

Regards,
Bob

Bob-san,

Thank you for your reply.
I wait the comment from the designer.

Best Regards,
Kuramochi

Hi, Kuramochi-san,

Update information so far, TPS2557 have two OTSD threshold(refer to 6.5 Electrical Characteristics in datasheet):
OTSD1 is for when the device is in current limit and is self-heating to a dangerous temperature. The OTSD1 will turn off the switch and the device temperature will fall. Clearly OTSD1 is valuable since it prevents the device from being damaged in a very common use condition.
OTSD2, however, is for when the ambient temperature has risen too high. If the ambient rises too much, OTSD2 will put the device into a minimum power dissipation mode and the junction temperature will fall back towards ambient. Of course, if the ambient temperature keeps rising, the junction temperature will also keep rising and the device can still be damaged.

So from what you said, your "When VBUS-GND are shorted, TPS2557-Q1 repeats OTSD and restart. So high temperature condition may keep during long term. My customer must show what the device doesn't damage on this condition for END customer. " So your customer are concerning about short to GND, which related to OTSD1. We can find the min OTSD1 is 135deg, so there's much margin between Abs Max Tj and max OTSD1. I know you and your customer still want to know Max OTSD1. Although there's no data in datasheet, I will ask designers about the value.

As far as OTSD2, You and your customer are definitely correct. I discussed with 810 designer and realize that we can't guarantee OTSD2 is below Abs Max Tj for 810. I am sorry for my assumption before. Design and manufacture may cause this different from part to part. Sometimes OTSD2 stays below Abs Max. Sometimes OTSD2 goes above Abs Max. I will ask the Max OTSD2 and Max Tj parameter from TPS2557 designers or margin between Max OTSD2 and Max Tj.


Regards,
Bob

Bob-san,

Thank you for your support.
How is progress about information we request?

Best Regards,
Kuramochi

Hi, Kuramochi-san,

1. Max OTSD will be around 20deg-30deg higher than min OTSD. So for TPS2557 short to GND case, the max OTSD1 threshold should be 165deg.
2. Max Tj should be around 180deg.
So your customer don't need to worry about chip damage when OUT short to GND.

3. For OTSD2, we can't guarantee OSTD2 below max Tj.

In all, I want to let you know that it will need lots of tests to get those specific value. So all above information is from our experience for your reference.

Regards,
Bob

Hi Bob-san,

Thank you for your information.

>3. For OTSD2, we can't guarantee OSTD2 below max Tj.

Tj max is specified "internal limited" on the datasheet.

Does it mean that this is untruth without current limit(OTSD1)?

Best Regards,
Kuramochi